Sound transmission circuits



Jan. 2, 1934. L. M. APPLEGATE 1,941,591

SOUND TRANSMISSION CIRCUITS Filed March 2, 1927 AMPLIFIERS MODULATORS OSCILLATOR Patented Jan.2, 1934 sons TRANSMISSION "C U T 1 l r r Lindsa y M. 'Applegate, Portland, Ore'g., assignor r ,gto ,John B. Brady, Somerset, Md.

, This invention relates genorally to transmission of sound, and specifically to the transmission of energy of sound frequencies in signal ciniaccomplishing the modulation of radio fretransmission systems. The purpose of this invention is to extendthe range of soundoraudio -frequencies that can be accommodatedby, modulated transmitters for transmitting signals,such

as musical programs requiring an extensive; range I Such programs require,

of sound freq lncies. for reasonably good reproduction, sound frequencies from about 50 to -about,.8,000 cycles per second. For perfectreproduction a transmitter shouldbe able to accommodate the entire audible range of sound lfrequencies whicn in the-case thel o s s t vah m n tisc d red to be a range of about 4 to 32,000 cycles per, second. The actual limitations; of individual instrumentalities for transmitting ,a broad; range ,;of sound frequencies ;are well known in the art. "This is, true particularly of sound transmission lines and transformers. Examples ,of ,such limitations arefound frequently in; audio transformers which will not usuallyoperatewith uniform effect over a range more extensive than from about 100 cycles per second to about 3,000cyc1es per second, or, expressed, asa iratio,zof one to thirty. ;Su'ch a transformer will usually operate with gradually decreasing effect both at the lower and uppenends of its frequency range beyond the frequencies stated. It appears to be practically impossible to; construct ;si'ngle sound transmission circuits thatwi lli accommodate with complete uniformity a range'of frequenciesi as great as that desired for reproduction ,of signals of the character of musical programs. j The limitatiorfofabout one to thirty mentioned above remains approximately the same regardless of the position of the range in the -venience.

3 In the operation of the invention shown, the 9;;

frequency scale. That is, a transformer can be designed with a range of from 1 to 120 cycles per second, or from 1,000 to 30,000, for example, but the ratio of the lowest to the highest frequency is more or less constant. J In view of the fact that single'sound circuits cannot accommodate all the frequencies to be desired in a signal, a, plurality of circuits, each accommodating a particular range of frequencies,

' would cover a range of from 20 to 18,000 cycles can be combined to accommodate the, entire range desired. For example, if a transformer for all the frequencies from 4 to 32,000 cycles per second were desired, three transformers, one having a range of from 4 to 80 cycles per second, one having a range of from 80 to 1,600 and one having a range of from 1,600 to 32,000 cycles per second, properly combined, would accom-' mod ate the entire range of frequencies of from 4 to.32,000.cyclespersecondi. Inmy invention this principle is made use .01

quencyuoscillationsover a broad range. of sound frequencies} the accompanying drawing, l illustrate my ranges or bands of sound frequencies; Three cir-.

.cuit'spthei first including an. amplifier 1, and a, coil .2, the 1.5600116. an. amplifier l '3 'and' two. coils 4 and 5;and the third an amplifierfi-anda coil 7, respectively accommodatezithe three bands of 7 "sound frequencis:A, -B, and 0,; which, collective- 1y, rprovide; for. acomparatively extensive range .of: sound'; frequencies. Energy 30f the .several frequency bands is delivered to the circuits shown from such appropriatecircuitsas may be desired. 7

These? since .theyare known to the art in various forms, are indicated in the drawing by three telephone.transmittersx8, '9, and: 10, of different sizes, the smallest one, 8, representing the higher frequencies, the middle: sized one, 9, the inter o -mediate:frquenciesyand' the largest one; 10, the

lower frequencies. The three "telephone transmitters together w are :intended' to accommodate :the entire range :of sound frequencies required for the reproduction. ofthe :signal concerned. 35

Coils 2 and4are parts 'of-a transformerll which also includes another'c'oil 12. Coils 5 and 'l are parts of a second --transformer 13 which has'a third coil 14. Coils 12 and 14 respectively connect with two modulators 15 and16 which'to- 9Q gethei modul ate the output of an 'oscillator 1'7.

The power source and usual connections, being well understood, have been omitted for conamplifiers 1, 3, and 6 have delivered to them energy of. the frequencies characteristic of the circuits preceding them. For example, circuit A may deliver energy of frequencies between 20 and about 210 cycles per second, circuit B frequencies 190 from 190 to 2,000, and circuitC frequencies from 1,800 to 18,000 cycles per second. Together they per second. In the frequency band limits stated, there is a certain overlapping, for example the A and B ranges overlap in the frequencies from to 210 cycles per second, and the B and C in the frequencies 1,800 to 2,000 cycles per second. This is necessary if a uniform effect of transmission over the entire range is to be obtained be- 9 600tf18;000 cycles per'second. the ratio 'ofitl'ie upper tothe lower frequencies cause the lines, transformers, and so forth, associated with the respective frequency bands accomplish uniform transmission only over a limited portion of their respective frequency ranges, and they decrease in effectiveness more or less gradually at their upper and lower limits. In these individual frequency bands the ratio of the upper to the lower frequencies is about to 1, while that of the total frequency range of the three in combination is 18,000 to or 900 to 1. The amplifiers 1, 3, and 6 deliver their energy to the transformers l1 and 13. Amplifier l clelivers all its energy to transformer 11 and coil 12 through coil 2. Amplifier 3 delivers part of its energy to transformer 11 through coil 4 andpart to transformer 13 through coil .5. Amplifier 6 delivers all its energy to transformer 13 and coil 14 through coil 7. Thus transformer '11 receives all the A" frequency energy'andpart of the B frequency energy, and transformer 13 receives; partof the B frequencyenergy and :themtwo. transformers 11 and 13: are correctly proportioned, coil 12 will carry frequencies from ;20i to'somewhat more than 600 cyclespersecond,

and coil 14 frequencies from somewhat less than In both coils is about to 1:.- The two coils 12 and 14 control respectively modulators 15 and '16 which, coacting, modulate the output of oscillator 17. through the entire range offrequenciesaccommodated -by-theseveral circuits,A,-.B, and C collectively.

Inthe-above explanation therespective ranges of frequencies of the three amplifier circuits weredescribed-bytheratioof 101 /2 to 1. Under some conditions, the amplifier circuits 'havesuch ranges individually that the frequency rangesof 'theitransformers- 11 and. 13 are the principal limitings' factors. Under such c'ondi-tionsfthe characteristics, of. the transformers determine the limits' 'ofthe frequency bands.

It'should be understood inrconnection with the drawing that the selection of three as the numberrofsamplif-ying circuits and two as the-number "of modulating circuits has been chosen arbitrarily for purposes of explanation'iand'illustration. Any convenient pluralitiesof amplifying circuits and modulating circuits can be used at will. Itshouldbe understood also that the par- .ticular form of connection shown between'the an oscillating circuit, a plurality of modulating eircuits operatively associated therewith, said modulating circuits. being individually operative for limited ranges of modulating frequencies, said limited ranges of modulating frequencies partially overlapping and together accommodating an extensive range of modulating frequencies, a plurality'of amplifying circuits operatively associated with saidmodulating circuits, said amplifying circuits being individually operative for limited ranges of modulating frequencies, said limited ranges together covering an extensive range of modulating frequencies, the number of modulating circuits being different from the number of amplifying circuits.

2. Inmultifrequency transformers, the combination of a plurality of primary circuits, a plurality of magnetic circuits, and a plurality of secondary'circuits, the number of which is different from the number of primary circuits, the

' whole being arranged so that said primary cirall of the C frequency energy. If the coils in cuit-s are adapted respe ctively to particular rangesof-frequencies, and said secondary circuits-adapted-to other particular ranges of frequencies, the said primary ranges of frequencies togethercomprising a wide range of fre-' as the primary, one-ofsaid secondary circuits receivingsubstantially all the frequencies of one of said primary circuits, another of said secondary circuits rece'iving substantially'all the frequencies of another of said-primary circuits, and

both of said secondary circuits receiving part of thefrequencies of a third of said primary circuits.

3. -In-mu1tifrequency transformers thecombination of a first *pluralityof elec'triccircuits arranged to accommodate, individually, limited ranges of frequencies partially overlapping, and,

collectively, accommodatingan extensive range of frequencies, a plurality of magnetic circuits less in number than the number of circuitsin the said'fi-rst plurality, and asecond plurality of electric circuits arranged to accommodate, individually, limited ranges of frequencies partially overlapping and, collectively, accommodating the same extensive range of frequencies as is accommoda'ted by the said first plurality of electric circuits, the whole being arranged so that'energy of the said extensive range of frequencies is transferred between said first plurality and 'said secon'd plurality of electric circuits, at least one electric circuit of said first plurality of electric. circuits dividing its energy between two of said magnetic circuits.

LINDSAY APPLEGATE. 

